Field of the Invention
The present invention relates to a current-voltage converter, a photoelectric conversion device, and a camera.
Description of the Related Art
A current-voltage converter (transimpedance amplifier) includes, for example, an operational amplifier and a feedback resistor provided on the path between the inverting input terminal and the output terminal of the operational amplifier. The non-inverting input terminal of the operational amplifier is fixed to a predetermined voltage. The current-voltage converter receives a current at the inverting input terminal and outputs a voltage corresponding to the amount of current from the output terminal. Such a current-voltage converter can be used to detect, for example, a current from a photodiode (that is, the amount of charge generated by photoelectric conversion).
As a feedback resistor, an element having a predetermined impedance, such as a resistor element or diode, can be used (see Japanese Patent Laid-Open No. 2000-315923). The gain of current-voltage conversion can be increased by increasing the resistance value of the feedback resistor. On the other hand, this makes the current-voltage converter easily oscillate. Some current-voltage converter has an input resistor provided at the inverting input terminal of an operational amplifier (see Japanese Patent Laid-Open No. 11-008517). Increasing the resistance value of the input resistor can make it difficult for the current-voltage converter to oscillate.
The above input resistor causes a potential difference based on its resistance value and an input current amount. For this reason, increasing the resistance value of the input resistor leads to the application of a voltage higher than expected to a current detection target (the photodiode in the above case), when the input current amount is larger than expected. As a result, the current detection target may be caused to perform an inappropriate operation. This is equivalent to that the range of input current amounts that allow the current-voltage converter to perform current-voltage conversion is narrow.